Hydrotherapy tubs which are also sometimes referred to as whirlpool baths have become increasingly popular in the last few years, particularly for home use. In the home, the operation of the tubs is, of course, not carried out under the supervision of trained personnel and parts can be damaged under certain conditions. For example, operation of the system without water present can damage both the pump and operating motor and other malfunctions can occur. Moreover, the water can overflow if the hydrotherapy pump is operated with the water at too high a level in the tub. Moreover, if it is necessary for the user to operate a standard electrical switch while sitting in the tub, there is the possibility of an electrical shock. While others have proposed electrical sensors having no moving parts that need only to be touched to operate the control switch, it has been the practice to provide a grounding plate which extends through the tub wall and/or connected to metal plumbing, which must be touched by the user in order to operate the switch. Such systems make the switch easier to use but may not completely eliminate the electrical shock hazard.
Other water control systems have been previously proposed. For example, U.S. Pat. No. 3,415,278 provides two antennas on the side of an earthenware sink, each connected to an oscillator, one of which operates the cold water valve and one of which operates the hot water valve.
U.S. Pat. No. 3,556,146 employs capacitor plates which are located near the faucets of a sink. Each sensor has two capacitor plates connected to an electrical circuit with Zener diode and an impulse generator. If a hand is placed near one of the capacitors, it is grounded, thus reducing the output voltage, thereby turning on or off hot or cold water valves.
U.S. Pat. No. 4,169,293 shows that it is known to provide a microswitch for controlling the pump of a hydrotherapy tub.
In view of the deficiencies of the prior art, it is a general objective to provide noncontacting sensors for controlling the pump operation of a hydrotherapy tub wherein installation is simplified by having no contacts that pass through the tub wall while at the same time more positively eliminating leakage and the possibility of electrical shock. Another objective is to provide a reliable noncontacting sensor which will operate with a positive action merely by placing the hand in proximity to it so that no physical contact is required. A further objective is to eliminate deficiencies of electrical sensors previously employed which were subject to contamination as the result of soap film deposits or mineral deposits on exposed metal sensing pins previously required to project through the tub wall and to come in contact with water present in the tub. A further objective is to provide a highly reliable noncontacting proximity sensor for hydrotherapy tub control which can be easily calibrated at the factory or during installation and requires no further attention by the user.
A further objective is to provide a combination protective circuit for pump operation which requires both a predetermined amount of water present and noncontacting actuation by the operator for the pump to be turned on.
These and other objects will be apparent in view of the following detailed description which sets forth the invention by way of example.